Add missing image file. Fix some formatting issues, spelling and awkward wording.

Build/NucleoTNC.ipynb

@@ -12,7 +12,7 @@
     "\n",
     "The Nucleo TNC can be assembled for about $25 in parts, assuming you already have a breadboard and hookup wire.  The bill of materials and the equipment needed to build and use the TNC are provided below in the *Bill of Materials* and *Equipment* sections, respectively.\n",
     "\n",
-    "Please joing the [Mobilindk Community](https://groups.io/g/mobilinkd) on groups.io to share your builds and for help troubleshooting and using it.  Send us pictures of your breadboards.  We would love to see your builds!\n",
+    "Please join the [Mobilindk Community](https://groups.io/g/mobilinkd) on groups.io to share your builds and for help troubleshooting and using it.  Send us pictures of your breadboards.  We would love to see them!\n",
     "\n",
     "This project is intended for amateur radio operators from beginners to advanced.  If you want to just dive in to building it without understanding the theory of operations, start at the overview and skip to the BOM and Assembly Instructions.  For those who wish to understand the theory of operation from an electrical perspective, we start with the *Schematic* and *Theory of Operation* sections after a brief overview.\n",
     "\n",
@@ -85,20 +85,20 @@
     "\n",
     "## Glossary\n",
     "\n",
-    "ADC - analog to digital converter. An electronic component that converts analog voltages to digital numbers.\n",
-    "APRS - Automatic Packet Reporting System. A packet radio system invented by Bob Bruninga, WB4APR.\n",
-    "BBS - Bulletin Board System. An online interactive computer system common before the advent of the Internet.\n",
-    "DAC - digital to analog converter. An electronic component that converts digital numbers to analog voltages.\n",
-    "DMM - digital multimeter.  A piece of test equipment used to check voltage, current, resistance, continuity, and possibly other electrical characteristics of electronic components and circuits.\n",
-    "EEPROM - electrically-erasable programmable read-only memory.  An integrated circuit for semi-permanent data storage.\n",
-    "I2C - a two-wire digital communications bus used by integrated circuits for inter-chip communication.  It contains a clock line (SCL) and a data line (SDA). https://en.wikipedia.org/wiki/I%C2%B2C\n",
-    "KISS - Acronym for *Keep it Simple, Stupid*.  A type of TNC defined by a minimal control interface.  This is in contrast to other modems that have a full human-readable command language.\n",
-    "LED - light emitting diode.\n",
-    "MCU - microcontroller unit. A microprocessor with embedded memory and peripherals.\n",
-    "PGA - programmable gain amplifier.  An amplifier whose gain can be set programmatically.\n",
-    "PTT - Push-to-talk. The mechanism for enabling the transmitter on a radio.\n",
-    "TNC - terminal node controller.  In our case it refers to a modulator/demodulator (a modem).\n",
-    "TRRS - Tip, ring, ring, sleeve. Short-hand for a 4-pole phone connector.\n",
+    " * ADC - analog to digital converter. An electronic component that converts analog voltages to digital numbers.\n",
+    " * APRS - Automatic Packet Reporting System. A packet radio system invented by Bob Bruninga, WB4APR.\n",
+    " * BBS - Bulletin Board System. An online interactive computer system common before the advent of the Internet.\n",
+    " * DAC - digital to analog converter. An electronic component that converts digital numbers to analog voltages.\n",
+    " * DMM - digital multimeter.  A piece of test equipment used to check voltage, current, resistance, continuity, and possibly other electrical characteristics of electronic components and circuits.\n",
+    " * EEPROM - electrically-erasable programmable read-only memory.  An integrated circuit for semi-permanent data storage.\n",
+    " * I2C - a two-wire digital communications bus used by integrated circuits for inter-chip communication.  It contains a clock line (SCL) and a data line (SDA). https://en.wikipedia.org/wiki/I%C2%B2C\n",
+    " * KISS - Acronym for *Keep it Simple, Stupid*.  A type of TNC defined by a minimal control interface.  This is in contrast to other modems that have a full human-readable command language.\n",
+    " * LED - light emitting diode.\n",
+    " * MCU - microcontroller unit. A microprocessor with embedded memory and peripherals.\n",
+    " * PGA - programmable gain amplifier.  An amplifier whose gain can be set programmatically.\n",
+    " * PTT - Push-to-talk. The mechanism for enabling the transmitter on a radio.\n",
+    " * TNC - terminal node controller.  In our case it refers to a modulator/demodulator (a modem).\n",
+    " * TRRS - Tip, ring, ring, sleeve. Short-hand for a 4-pole phone connector.\n",
     "\n",
     "\n",
     "## Schematic\n",
@@ -203,7 +203,7 @@
     "\n",
     "### Audio Input\n",
     "\n",
-    "The audio input has a nominal peak-to-peak voltage limit of 3.3V.  To achieve good decode performance, it needs a nominal 200mV peak-to-peak input level.  However it can work with input levels much lower than this.\n",
+    "The audio input has a nominal peak-to-peak voltage limit of 3.3V.  To achieve the best decode performance, it should have at least 200mV peak-to-peak input level.  However it can work with input levels much lower than this.\n",
     "\n",
     "The audio input circuit starts with a DC-blocking capacitor and a programmable DC-offset section required to set the proper DC bias for the audio section. This programmable DC offset is required because there is an additional component of the audio input circuit that is not apparent in the schematic.  There is a built-in programmable gain amplifier (PGA) in the MCU that is used and this requires varying DC offsets depending on the gain selected.  The gain is selectable from 0dB, 6dB, 12dB, 18db, & 24dB.\n",
     "\n",